1. Field of the Invention
The present invention relates to the calibration of a variable-colour light source that allows the provision of coloured light of a selectable brightness and/or colour by means of a plurality of individually controllable light sources.
2. Description of Related Art
Colour light sources for generating light of variable colour and/or intensity are widely used in the entertainment industry, e.g. for stage illumination etc., and for other purposes within lighting design, e.g. to provide lighting effects in architecture, etc.
Typically, such variable colour light sources comprise a plurality of individually controllable light sources such that each individually controllable light source emits light of a predetermined colour. For example, in an RGB system, the variable-colour light source may comprise individually controllable light sources of the most common primary colours—red, blue, and green. By controlling the relative brightness of the respective individually controllable light sources of the different primary colours almost any colour in the visible spectrum may be generated by means of an additive mixing of the respective primary colours, resulting in output light of the desired colour and intensity.
US20040160199A1 describes lighting units of a variety of types and configurations, including linear lighting units suitable for lighting large spaces, such as building exteriors and interiors. Also provided herein are methods and systems for powering lighting units, controlling lighting units, authoring displays for lighting units, and addressing control data for lighting units.
US20050134202A1 concerns a light source having N light generators, a receiver, and an interface circuit. Each light generator emitting light of a different wavelength, the intensity of light generated by the light generator is determined by a signal Ik coupled to that light generator. The receiver receives a color coordinate that includes N color components, Ck, for k=1 to N, wherein N is greater than 1. The interface circuit generates the Ik for k=1 to N from the received color components and a plurality of calibration parameters. The calibration parameters depend on manufacturing variations in the light generators. The calibration parameters have values chosen such that a light signal generated by combining the light emitted from each of the light generators is less dependent on the manufacturing variations in the light generators than a light signal generated when Ik is proportional to Ck for k=1 to N.
U.S. Pat. No. 6,967,448 discloses a multi-colour LED-based light assembly, where different coloured LEDs are individually controlled by means of respective pulse width modulated current control. For instance, this prior art system allows a user to control such a variable-colour light source to generate light at different colours by means of three individual potentiometers, each controlling LEDs of a respective colour.
However, due to the varying characteristics and potential non-linearity of the individual light sources, it is difficult to obtain a precise colour control at different brightness values. This typically requires a cumbersome manual adjustment of the individual sources or a complicated and costly feed-back control of the light sources. For example, it is cumbersome to control the individual potentiometers such that the overall brightness of a variable-colour light source assembly is varied while keeping the colour (e.g. the hue and saturation) constant.
WO 2006/091398 concerns a manufacturing process for storing measured light output internal to an individual LED assembly, and an LED assembly realized by the process. The process utilizes a manufacturing test system to hold an LED light assembly at a controlled distance and angle from the spectral output measurement tool. Spectral coordinates, forward voltage, and environmental measurements for the as a manufactured assembly are measured for each base color LED. The measurements are recorded to a storage device internal to the LED assembly. These stored measurements can then be utilized in usage of the LED assembly to provide accurate and precise control of the light output by the LED assembly.
The WO document describes a linear relation for a LED in that a baseline is found during calibration. The behaviour of the LED is predicted from the baseline. This prediction can only for a limited use of the LED, because LEDs are unlinear components. Further, it is not effective to calibrate LEDs during the manufacturing process, simply because the internal heating in the LED depends of the actual cooling. An effective calibration can therefore first be performed after the LED is in operation in the actual use.
WO 2006/091398 was filed but not published before the filing date of the pending application.